The present invention relates generally to the chlorination of organic compounds and particularly to the catalytic chlorination of bromine-containing organic halides.
The conversion of bromine containing organic halides to other commerically useable forms by the replacement of at least one bromine atom with a chlorine atom is desirable in many instances. For example, in the preparation of the chain transfer agent bromotrichloromethane (CBrCl.sub.3) by the direct bromination of chloroform, the overbromination of the chloroform can result in the production of undesirable quantities of dibromodichloromethane (CBr.sub.2 Cl.sub.2) and tribromochloromethane (CBr.sub.3 Cl) as by-products. Preferably, these by-products are converted to the bromotrichloromethane product by a subsequent chlorination process. Similarly, the chlorination of 1,2-dibromoethane (CH.sub.2 BrCH.sub.2 Br) to form molecular bromine and a partially chlorinated haloalkane is quite common. The latter chlorination is generally catalyzed by the use of an iron halide or aluminum halide catalyst as described in U.S. Pat. Nos. 4,044,113 and 3,961,033. Such catalyzed processes are undesirable in many applications because of the incomplete displacement of bromide ions by chloride ions or because the molecular bromide and partially chlorinated products cannot be readily distilled from the catalyst.
It has now been found that organic halides containing at least one bromine atom can be chlorinated by a novel catalytic process.